Quark and gluon jets at LEP

• Main Author: Parsons, Mark Ian
• Published: University of Edinburgh 1994
• Subjects: 535
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.660369

Using the large number of hadronic decays of the Z° particle recorded by the ALEPH detector at LEP between 1990 and 1992, a study of the properties of a sample of these events has been made. High transverse lepton tagging has been used to identify the quark jets in three jet events. Evidence is shown that the angular distribution of the identified quark jets is described well by the theory of quantum chromodynamics. Using a log-likelihood statistical test a confidence level of 97% is obtained for the data to be in good agreement with JETSET Monte Carlo. An Abelian scalar gluon model is excluded. A separate study using symmetric three jet events and the same quark jet identification method is presented. This study compares quark and gluon jets in a configuration designed to minimise experimental biases. Gluon jets, when compared with a mixed flavour quark jet sample, are found to have a higher average charged track multiplicity ratio N<SUB>g</SUB>/N<SUB>q</SUB> = 1.62 ± 0.051 (the error is predominantly statistical). Evidence is also presented that they have a wider jet profile and that their particle energy spectrum is softer.